The lithium secondary battery, due to advantages of high energy density, high operating voltage, low self-discharge rate, and long storage life, has become a battery system that has gained a lot of attention in recent years. The lithium secondary battery is widely used in portable electronic application products such as mobile phones, tablet PCs, and digital cameras. Early lithium batteries used lithium metals for anodes, intercalation compounds composed of transition metal oxides for cathodes (such as LixCoO2 and LixMnO2), and non-aqueous organic electrolyte solutions containing lithium ions for electrolytes. After the battery is discharged a plurality of times, dendritic crystals are easily formed on the anode of the battery, causing the separator used to separate the cathode and anode materials to become easily punctured, which may lead to a short circuit. Moreover, the battery will heat up faster, causing a decomposition reaction of the electrolyte solution and the cathode material, which in turn causes dangers such as fire and explosion.
Therefore, the electrode surface of the lithium secondary battery needs to have a protective layer to prevent direct contact with the electrolyte solution and to suppress delithiation of the electrode and side reactions of the electrolyte solution. In the techniques of the prior art, the categories of the protective layer of the cathode surface are metal (such as Ag), metal oxide (such as Al2O3 and ZrO2), metal fluoride (such as AlF3 and ZrF2), and a plurality of carbon composites (such as graphene). An organic material is coated on the surface of the cathode in all of the categories. Moreover, the fabrication process of the coating is complex, and the cost is high. It is acquired that, the desired protective layer of the electrode surface of the lithium secondary battery not only needs to facilitate electrochemical property and thermal stability, but also needs to improve the cycle life of the battery at high temperature. Moreover, the fabrication process needs to be simplified to reduce costs.